The present invention relates to an arrangement for the automatically controlled changing of the valve timing of an internal-combustion engine, having at least one camshaft which can be turned relative to a shaft which drives the camshaft, as a function of parameters of the internal-combustion engine. The arrangement has a wheel which drives the camshaft, carries a first toothing and, by means of a coupling member which is acted upon on both sides by an oil circulating system and is axially shiftable between at least two end positions, acts upon a second toothing connected with the camshaft via the hollow shaft. The arrangement also has chambers bordering on the coupling members, the filling and emptying of which is controlled by at least one locking element.
It is known to adapt the valve timing of an internal-combustion engine to its rotational speed in order to be able to optimally operate it in a rotational speed range that is as broad as possible. As a result, the torque, the performance, the exhaust gas emission, the idling characteristics and the fuel consumption can be improved.
One possibility of changing the valve timing during the operation of the internal-combustion engine consists of turning, by means of a so-called phase converter, preferably the intake camshaft in its position relative to the crankshaft which drives it. In this case, as a function of the oil pressure, a coupling member, which is coaxially arranged between the wheel driving the camshaft and the camshaft, is axially shifted. The coupling member carries two toothings of which at least one is helical and which interact with one corresponding toothing respectively on the camshaft or in the wheel, as known, for example, from the European Patent Document EP-0 335 083.
Phase converters are known, for example, from the European Patent Document EP-0 245 791 having a coupling member that is shifted from a first end position into a second end position and vice versa by means of a piston which is hydraulically acted upon on both sides. The piston is surrounded by an annulus divided into two control chambers which interact with a control valve via oil-carrying bores. On the one hand, this valve controls a pressure oil flow into one of the two control chambers in order to displace the piston from one end position into the other end position. On the other hand, the valve opens the oil return flow from the second, unpressurized control chamber into a tank. This phase converter requires additional space in the axial direction of the camshaft because the adjusting path of the piston is arranged completely outside the camshaft.
From the already mentioned European Patent Document EP-0 335 083, a phase converter of the above-mentioned type is known in which the control of the oil flow takes place by means of a control element which is arranged in a flanged shaft screwed to the camshaft. This control element is axially shifted by means of a solenoid and guides the oil flows to and from the control chambers in a manner analogous to the mentioned European Patent Document EP-0 245 791. The flanged shaft and the solenoid lengthen the camshaft and require additional space. In addition, the manufacturing of this phase converter is complicated and expensive.
It is an object of the present invention to provide an arrangement for changing the valve timing of an internal-combustion engine which avoids the above-mentioned disadvantages, requires as little space as possible and has a simple construction.
This and other objects are achieved by the present invention which provides an arrangement for the automatically controlled changing of valve timing of an internal-combustion engine, comprising an oil circulating system and at least one camshaft which can be rotated relative to a shaft driving the camshaft as a function of parameters of the internal-combustion engine, this camshaft being coupled to a hollow shaft having a second toothing. The camshaft has an axially extending recess and a first bore that is connected to the oil circulating system. The arrangement also has a coupling member which is acted upon on both sides by the oil circulating system and is axially shiftable between at least two end positions, and a wheel which drives the camshaft and carries a first toothing. This wheel acts via the coupling member upon the second toothing that is connected with the camshaft via the hollow shaft. First and second chambers border the coupling member, and there is at least one locking element which controls filling and emptying of the coupling member. The arrangement includes a cylindrical body in one end of the camshaft that in the axially extending cylindrical recess separates a ring-shaped exterior space. This space, in a first position of the locking element, connects the first chamber with the first bore of the camshaft during filling of the first chamber.
The present invention permits a compact construction of the phase converter and a simple design of the drive-side end of the camshaft. This is achieved by taking the locking element controlling the feeding and removal of oil out of the phase converter or the camshaft. The locking element may be arranged at any arbitrary point of the internal-combustion engine, for example, in the cylinder head and is also actuated hydraulically.
In a graduated, axially extending recess of the camshaft which is easy to manufacture, a pipe is held which separates two spaces from one another which, according to the position of the locking element, permit the feeding or the removal of oil in the camshaft or the phase converter. The spaces are connected with radial bores of the camshaft which, in turn, interact with pipes which lead into annuli of the locking element, which in certain preferred embodiments is a change-over valve.
The radial bores may be arranged at any arbitrary point of the camshaft.
The phase converter projects only slightly beyond the drive-side end of the camshaft and can be mounted as a complete constructional unit. When no phase converter is to be mounted, the camshaft may also be used by the fastening of a changed sprocket wheel.
The camshaft, which is normally made of a hard material, requires no toothing or thread.
The arrangement of the present invention requires only a small amount of oil because only the oil displaced from the chambers adjacent to the piston must be replaced for the shifting of the piston from a first end position into a second end position.
The emptying of the chambers after the switching-off of the internal-combustion engine is avoided in the present invention by providing oil-carrying pipes that are constructed as ascending pipes which prevent an oil return flow.
The actuating circulating system for the changing of the valve timing is part of the oil circulating system of the internal-combustion engine. The lubricating circulating system for the camshafts is connected to this actuating circulating system in such a manner that, when the phase converter or the locking element fails, the lubrication is maintained.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.